Perform a flare system purge gas optimization study for a major international oil refinery in the Middle East.
REFINERY FLARE SYSTEM PURGE GAS OPTIMIZATION STUDY
The client, an international engineering services company, contracted Process Engineering Associates, LLC (PROCESS) to perform an optimization study for purging of the flare system for the ultimate refinery client located in the Middle East. The goal of the project was to identify a set of changes required to help minimize purge gas rates while maintaining safe operation of the ultimate client’s flare and flare header system. More specifically the following major items were performed:
1. Reviewed and evaluated current system operation and limitations
2. Identified improvement opportunities, identified suitable process alternatives, and quantified the expected process benefits and impacts of each alternative. This included the following:
- Flare system velocity profile analysis
- Flare gas BTU analysis and control systems review
- Flare system steam flow analysis and control systems review
- Investigation and analysis of process source leakage into the system
- Operational requirements affecting purge rates
- Sour services/sweeping/cooling effects on minimum purge rates
- Global relief scenarios such as area fire, loss of cooling systems, etc.
- Suggested recommended improvements.
At the initiation of the project task, PROCESS obtained the requisite process and engineering information from the client. Using isometric drawings, PROCESS constructed a detailed computer simulation of the refinery flare system using its licensed commercial computer process simulation software, Flarenet. Relief streams’ composition and thermodynamic properties were used to evaluate the flare gas BTU analysis, make-up gas rates, and flashback prevention minimum purge rate. In addition, the required purge rate was evaluated at different rates of volume contraction due to sudden cooling or hot relief events. PROCESS used the flare system simulation to obtain velocity profiles based on the current fuel gas purge rate, and to optimize the purge rates to meet the minimum requirements for the existing flares.
A list of relief valves and pressure control valves that discharge to the flare headers was generated; the leakage rate was calculated based on control valve specification and API Standards for leakage rates of relief valves. The leakage rate was combined with the current purge rate to obtain the annual cost of gas that is purged. PROCESSrecommended changes to better control purge gas rate as needed, and also recommended changes to the flare tips in order to reduce the minimum required purge gas rates.
A project report was provided to the client that contained detailed calculations, a tabulated summary of leakage rates, a tabulated summary of the purge rates and velocities, a tabulated summary and graphs of the rate volume contraction due to cooling, a budgetary cost of new flare tip, a budgetary cost of a flare gas recovery unit, and a working copy of the simulations.
- Petroleum Refining
- Flare system design and analysis